The PIs propose to develop novel micro- and nano-fabricated systems that can be used to monitor the simultaneous and competing effects of physical and chemical guidance cues on cell behavior. In particular, this work will focus on understanding how different types of signals "compete" to give rise to axonal extension from neurons. Many groups have studied the impact of different factors individually or in combination, but no one, to our knowledge, has looked at competition between individual factors and combinations of factors. This information will shed insight into the effect of external signals on polarization events and axonal guidance mechanisms involved in development and nerve regeneration, and could potentially provide insight into the desirable characteristics for therapeutic systems to aid nerve repair. To test how different signals contribute to neurite extension, micro- and nano-fabrication techniques will be used to create unique patterned geometries that simultaneously, and yet independently, present the neuron with physical or mechanical cues (e.g., grooves, pillars) and chemical cues (e.g., growth factors, adhesive ligands). In particular, the competition between grooved substrates and immobilized nerve growth factor and netrin-1, and combinations of these stimuli, will be studied for both polarization (axon initiation) and axon elongation and steering responses. Three different device geometries will be fabricated: (1) a "parallel" geometry to test polarization and decisions made at the cell body in response to competition between two stimuli, (2) a "cross-shaped" pattern to test polarization and decisions made at the cell body in response to competition between three or more stimuli, and (3) a "branched" pattern to test axon guidance and decisions made at the growth cone in response to two or more stimuli. Rat embryonic hippocampal neurons will be precisely micropositioned on the devices such that they have equal probability of encountering each separate cue. This will allow the cells to make "decisions" between competing factors by either defining an axon or extending an existing axon toward a desired signal. Image analysis and fluorescence microscopy will be used to measure neurite elongation and monitor the presence of axonal and dendritic markers in response to each cue. The three different proposed devices will be fabricated and optimized as part of Specific Aim 1 and the effects of signal competition on polarization and axon steering in rat hippocampal neurons will be assessed in Specific Aims 2 and 3, respectively. [unreadable] [unreadable]